Project Summary Traumatic brain injury (TBI) is a devastating neurological injury afflicting over 1 million people annually, including a large number of young adults and military personnel. Cerebral edema is associated with increased intracranial pressure (ICP) and a poor clinical outcome following TBI, although the cellular mechanisms underlying this process remain unknown. This gap in the understanding of cerebral edema formation contributes to the lack of clinically- effective therapeutics for TBI patients. Recent work by our laboratory demonstrates that acute neuronal necrosis stimulates the passive release of high mobility group box protein 1 (HMGB1), which in turn induces glial swelling and cerebral edema. Specific Aim 1 will establish whether activation of individual NMDA receptor subunits increase neuronal injury and cerebral edema following experimental TBI. The incorporation of NR2A and NR2B knockout mice will determine whether individual NR2 subunits contribute to HMGB1 release, brain swelling, and neurological outcome using following head trauma. Specific Aim 2 will determine whether toll-like receptor-4 (TLR4) mediates the pro- inflammatory and cerebral edema promoting effects of HMGB1. The ability of HMGB1 to stimulate the astrocytic water channel, AQP4, will also be addressed in TLR4 mutant mice. Specific Aim 3 will determine whether HMGB1 may represent a novel biomarker to predict the development of cerebral edema folowing head trauma in humans. Measurement of HMGB1 levels within the cerebrospinal fluid (CSF) and serum of neurotrauma patients will be correlated with acute neuronal injury and neurological outcome. Together, the proposed studies will investigate the novel possibility that HMGB1-TLR4 signaling contributes to the development of cerebral edema and increased ICP following TBI. The results of these studies may support the future development of novel therapeutics directed against this pathway to limit neurological injury following head trauma.